Experimental Studies on Wake-Induced Bypass Transition of Flat-Plate Boundary Layers under Favorable and Adverse Pressure Gradients

Abstract

This study investigates wake-induced bypass transition of boundary layers on a flat plate which is subjected to favorable and adverse pressure gradients. Inlet free-stream turbulence level is controlled with a turbulence grid. Detailed boundary layer measurements are executed by use of a single hot-wire probe. The main focus of this paper is on how and to what extent the wake-induced bypass transition of a flatplate boundary layer can be affected by favorable - adverse pressure gradient as well as enhanced turbulence intensity. A spoked-wheel-type wake generator creates periodic wakes in front of the flat plate. Two types of the wakes are generated by altering the direction of the movement of the wake-generating bars. Instantaneous velocity signals successfully reveal the flow events associated with the wake passage happening inside the boundary layer, such as the emergence of turbulent spots and calmed regions behind them. Noticeable differences in the transitional behavior due to the wake passage also appear between these two types of the wakes.